I've been keeping a partial record of which side won for the games I've played recently.
Town: 44 40.37%
Mafia: 46 42.20%
Cult: 12 11.01%
Serial Killer: 3 2.75%
Arsonist: 2 1.83%
Witch: 2 1.83%
Total: 109 100.00%
Roughly 40% Town, 40% Mafia and 20% Neutral. MM only appeared like 5 times in these 109 games and none of them won.
Personally I find Cult the easiest to win as if you pick the right people to recruit.
Here we are after about 100 more games. Seems like the percentage for Town and Mafia didn't change much. Still yet to see a MM win.
Town: 83 40.49%
Mafia: 82 40.00%
Cult: 17 8.29%
Serial Killer: 12 5.85%
Arsonist: 8 3.90%
Witch: 3 1.46%
Jester: 1 0.49%
Total 205 100.00%